The invention relates to a hub wheel assembly having shock absorber means for use on light load bearing vehicles. More particularly, the invention relates to swivel-mounted tandem wheel assemblies with shock absorbing means particularly adapted for use on movable vehicles such as infant strollers, baby carriages, carts or wheelchairs.
Most movable vehicles for light-load duty, including those of infant carriers, employ relatively simple methods of securing the wheel systems to the vehicle chassis. Most commonly, each leg or strut of the vehicle chassis is connected to a single wheel mounted on a rigid bracket. The bracket is typically U-shaped to extend down on either side of the wheel to support the extreme ends of an axle disposed through the wheel hub. To provide maneuverability, wheel systems are typically pivotably mounted to the frame of the vehicle. As such, the wheel can swivel freely when an angular force is applied to the vehicle to pivot or steer the wheel in the desired direction of motion. One embodiment of this type of apparatus is shown in U.S. Pat. No. 3,653,681 to Virtue.
Prior art single-wheel apparatus have several disadvantages. For example, a single wheel swivel-mounted to a rigid frame tends to track poorly when exposed to lateral forces. Many swivel-mounted wheel systems are attached by a single rivet point which causes the wheel to shimmy and wobble when exposed to uneven surfaces and propelled in a non-linear direction. Even when ball bearing surfaces are employed, when a force perpendicular to the orientation of the wheel is applied, the wheel tends to bind and skid sideways rather than rotate in the direction of the angular force.
In an attempt to add stability and tracking qualities to light load vehicles, tandem wheel assemblies have been employed. Tandem wheel arrangements for carts and carriages are well known in the art. For example, U.S. Pat. No. 3,967,342 to Gebhard discloses a swivel wheel arrangement for baby carriages having a tandem wheel system with one wheel mounted on either side of a central spindle. The device uses a central spindle assembly having a vertical shaft rotatably mounted in an upper sleeve. The apparatus uses a pair of mounting plates disposed on either side of the sleeve and secured to the shaft with a pin. The wheels are connected to the free end of the plates by an axle assembly. A resilient flexible ring is secured between the two mounting plates and restricts the rotation of the plates about the centralized pin. Although an improvement over the single-wheel systems, this device still has several disadvantages.
One disadvantage is that the centralized shaft is rotatably mounted into a sleeve and does not employ any type of ball bearing surfaces. The weight-bearing engagement between the upper sleeve and a shoulder associated with the central spindle provides a rotatable contact surface between the two elements. This type of arrangement is prone to wear and binding contaminants entering through the spindle region and inhibiting rotation between the spindle and the sleeve. Additionally, the relatively large surface area in rotational contact is prone to increased friction when exposed to the lateral loads common in this type of carriers. Additionally, the resilient pad mechanism used for suspension is insufficient. Very limited travel is available and the resulting device does little to smooth out the resulting ride.